1. Field of the Invention
The present invention relates to a wideband radio access system, and more particularly, to a method of transmitting and receiving a random access request (random access preamble) and transmitting and receiving a random access response in a wideband radio access system.
2. Discussion of the Related Art
In a technology related to a wideband radio access system, each user equipment may attempt to access the system with a randomly selected sequence or opportunity in each random access channel (RACH) slot. A base station detects a random access sequence (or an RACH sequence) and then transmits a random access response (or an RACH response). Each user equipment receives the random access response from the base station, considers a response including its sequence as its response, and performs a timing advance operation.
In the technology of this field, each user equipment may attempt to access the system with a randomly selected sequence or opportunity in each RACH slot. A base station detects the RACH sequence and then transmits a response thereof. Each user equipment receives the RACH response from the base station, considers a response including its sequence as its response and performs a timing advance operation. At this time, if an accurate time interval is not present when each user equipment waits for the response, each user equipment may erroneously receive a response of another user equipment as its response. This state is shown in FIG. 1A. FIG. 1A is a view showing an example of an RACH response (random access response). This state may appear in all RACH periods. Referring to “3GPP TS 36.211 v.8.1.0, ‘Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation’, 2007 Dec. 20” regarding to random access in a wideband radio access system, a table for a random access preamble format, a random access preamble parameter and random access preamble timing for preamble formats 0 to 3 is described. FIG. 1A shows an RACH slot having a period of 1 ms and a preamble format of 0.
In FIG. 1A, a first user equipment 1 attempts access with a randomly selected sequence 1 in an uplink (UL) subframe 0 (S110). In an uplink subframe 1, a second user equipment 2 attempts access with a randomly selected sequence 1 (S120). If a base station detects the sequences of the two user equipments, the base station transmits responses of the detected sequences (S130). At this time, the two user equipments 1 and 2 which attempt access wait for their responses. When the response of the sequence 1 is reached in an uplink subframe 7, both the user equipment 1 (UE1) and the user equipment 2 (UE2) may determine that the response reached in the uplink subframe 7 is the response for their sequence. In this case, one of the two user equipments erroneously determines that the response reached in the uplink subframe 7 is its response. Since the two user equipments perform time synchronization by the response received in the uplink subframe 7, one user equipment performs erroneous time synchronization. In addition, since data or a control signal is transmitted again in uplink using the same resource indicated by the response, a problem that the two user equipments use the same resource occurs.
In FIG. 1 and the description related to FIG. 1, a cell radius is not considered in order to facilitate the understanding of the problems of the technology related to the present invention. However, if the cell radius is actually about 50 km and the propagation speed of an electromagnetic wave is considered, a random access preamble transmitted by the user equipment 1 in the uplink subframe 0 may reach the base station in a downlink subframe 0 or a downlink subframe 1, and a random access preamble transmitted by the user equipment 2 in the uplink subframe 1 may reach the base station in a downlink subframe 1 or a downlink subframe 2. In addition, a random access response transmitted by the base station in the downlink subframe 1 may reach the user equipment 1 and/or the user equipment 2 in the uplink subframe 1 or an uplink subframe 2 and a random access response transmitted by the base station in the downlink subframe 2 may reach the user equipment 1 and/or the user equipment 2 in the uplink subframe 2 or an uplink subframe 3 (see FIG. 1B).
Unlike the above example, if a resource available in a time domain in which the base station transmits the response is not present, a problem that the response cannot be transmitted on time occurs. In this case, the response of the RACH slot is not transmitted or is delayed. At this time, there is a need for a method of distinguishing between a delayed response and a response which is transmitted on time or between delayed responses.
In addition, if responses of several RACH slots are collected and are simultaneously transmitted, there is a need for a method of distinguishing between RACH slots.